Large size pneumatic tires, ordinarily referred to as "off-highway tires", are usually mounted on substantially cylindrical wheel rims having one fixed flange and one removable flange. Prior to the present invention, however, a process and apparatus were developed as shown in U.S. Pat. Nos. 3,489,198 and 3,612,140, which made it feasible to utilize tires and rims of the drop-center type.
This prior apparatus uses a rim support which holds the lower flange of a rim by clamps; a tire is positioned with a portion of its bead inserted below the upper rim flange; and an external thrust-applying mechanism, spaced from the rim support platform, drives this portion of the bead into the drop center of the rim. Adjacent to the center of the rim support platform are two side-by-side vertical shafts whose lower ends have gears between which a two-sided rack moves linearly, to rotate the shafts simultaneously in opposite senses. This lower end mechanism is fixed in its vertical position. Secured to splined upper ends of the vertical shafts are rotating bead-deflector arms. The splines permit setting the arms at heights corresponding to the height of the upper flange of the rim above the platform, to accommodate variations in the width of the rims.
Since the shafts of this prior art apparatus are not at the geometric center of the arm, the arms which carry the bead deflectors are designed to telescope, with their inner surfaces riding around against the outer edge of the upper rim flange. The resulting friction increases the power required.